Silicone elastomer system having biocide properties useful in particular for making impressions in dentistry

ABSTRACT

An elastomer system having biocide properties is described, useful, in particular, for dental impressions. An efficient system is provided for destroying microbes, without adversely affecting the crosslinking properties and the mechanical qualities of RTV 2 elastomers. Said system comprises an RTV 2 silicone, preferably SiH/SiVi polyaddition product and a biocide selected among active chlorine precursors, preferably among N-chloramines. The system may include functional additives (silicon fillers, alumina, paraffin, vaseline oil). As for the biocide, it can be provided with an antiseptic auxiliary adjuvant along with EDTA-type sequestering agents.

The field of the present invention is that of organosilicon systemscomprising a polyorganosiloxane composition which can be hardened intoan elastomer and at least one biocidal active ingredient chosen fromchlorine derivatives. The applications targeted by such systems are inparticular the taking of impressions and, still more particularly, thetaking of dental impressions in the context of the production ofprostheses.

The present invention therefore relates to a silicone elastomer systemhaving biocidal properties and which can be used in particular for thetaking of impressions, for example dental impressions.

The subject of the invention is also a material for taking impressions,in particular dental impressions, comprising the abovementioned siliconeelastomer system.

Finally, the invention is aimed at the use of the system or of thematerial for the taking of impressions, for example dental impressions,as well as a process for preparing the said system and/or the saidmaterial.

The notion of biocidal activity relates to the fields of hygiene,comfort and medical and paramedical applications. The use of siliconeelastomers is very widespread in these fields. This is partly due to thefact that silicone elastomers offer, on the one hand, a wide diversityof chemical, mechanical and physical characteristics, and, on the otherhand, a nontoxic, nonirritant and nonallergenic character. In addition,silicone elastomers constitute poor culture substrates formicroorganisms, which confers on them remarkable properties with regardto hygiene.

It is moreover known that silicones of the cold-vulcanizable elastomertype which advantageously exist in the form of two components (EVF 2 orRTV 2) are particularly suitable for the art which consists in takingimpressions, in reproducing and in creating forms. This is explained bythe fact that these silicones are endowed with properties of fluidityand film-forming ability before crosslinking, which makes possible thetaking of an impression of any model or of any form. The subsequentcrosslinking which causes the hardening of the silicone elastomer makesit possible to constitute suitable moulds from the impressions. The goodthermal stability of the crosslinked EVFs (or RTVs) allows the mouldsmade from these materials to withstand the high melting points ofcertain moulding materials such as metals.

The production of moulds from EVF or RTV silicone elastomer isparticularly advantageous in order to obtain small series for which thecost and the period of production of the mould are not excessive, unlikewhat is observed when the mould is metallic.

There is a link between this “moulding” application of EVFs or RTVs andtheir use in the health field since dentists, chiropodists and plasticsurgeons use silicone elastomers to produce moulds for dentures or forcorrective forms (inserts, breast prostheses).

Thus, without limitation, EVFs or RTVs are particularly advantageous inthe field of the taking of impressions, in particular dentalimpressions, because they are available in the non-crosslinked stateunder fluid- or paste-type rheologies. Moreover, they crosslink within afew minutes at room temperature; they are nontoxic and satisfy Europeanregulations in the pharmaceutical field. However, the taking ofimpressions remains subject to surface or even intermass contaminationsby pathogenic microorganisms and thus becomes vectors for propagationand dissemination of microbes between the dental practice and theprosthetist's laboratory.

To attempt to counteract this, it is possible to conventionally carryout a disinfection treatment of the impression material by bringing itinto contact with a conventional antiseptic, for example by immersion orby spraying. This type of disinfection treatment limited to the surfaceis of course not completely without efficacy in the desired attempt tobreak the contamination chain, but it remains totally inadequate. Inaddition, this additional step of surface disinfection represents aconstraint which practitioners can gladly do without.

In the context of a search for efficacy in the area of decontaminationof these materials for taking dental impressions in particular, thesolution consisting in incorporating into the material itself anantiseptic which will perform its primary function both intermass and atthe surface, is also known. By way of illustration of this technicalproposition, there may be mentioned European patent application EP No. 0361 301 which describes the introduction of a biocide into analginate-based material for taking dental impressions. Alginates are ahardly convincing alternative to the EVFs or RTVs. The biocidal agentinvolved exists in the form of an aqueous solution of quaternaryammonium salts and of compounds based on guanidine and its derivatives.This solution replaces the water necessary for the preparation of thealginate paste.

There is also known outside the specific application “taking of dentalimpressions” but still in the context of the biocidal siliconeelastomers used in the hygiene and health field, European patentapplication EP-A-0 493 186 which describes a biocidal organosiliconsystem comprising:

a two-component organopolysiloxane composition which can be crosslinkedat room temperature or in the presence of heat, by in particularpolyaddition reactions,

as well as a biocidal system consisting of a salt of a hydracid or of aninorganic oxacid or of an organic acid derived from a linear polymericbiguanide: poly(hexamethylene-biguanide). This silicone elastomer withbiocidal activity is intended to be incorporated into sponges so as tocombat bacterial proliferation both during the period of storage andduring the period of use of the said sponges.

There should also be mentioned in this review of the prior art Frenchpatent application 93 08 114 published under No. 2 707 660 and whichrelates to a silicone elastomer system obtained by crosslinking acomposition comprising:

A—100 parts by weight of α,ω-di(hydroxy)diorganopolysiloxane silicone;

B—from 2 to 20 parts by weight of a crosslinking silane containing ahydrolysable group;

C—from 0 to 150 parts by weight of an inorganic or organic filler;

D—1 to 150 parts by weight per 100 parts of A+B+C, of a solid inorganicor organic compound capable of releasing active chlorine in contact withwater or moisture (preferably calcium hypochlorite);

E—optionally a polycondensation crosslinking catalyst.

This composition contains at least 0.01% of its weight of water providedand optionally generated intrinsically and optionally providedextrinsically. In this patent application, the use of such a system asagent for releasing active chlorine, in particular for the treatment ofwater, is recommended.

The elastomer silicone system according to this patent application isstrictly limited to the silicone of theα,ω-di(hydroxy)diorganopolysiloxane type which is crosslinkable bypolycondensation. In addition, the silicone elastomer system disclosedin this patent application is described as being capable of being usedfor the production of seals or of films useful in the fields of hygieneand of sanitary applications. Another application envisaged in thisprior art reference is that of the treatment of water. The system is inthis case provided in the form of silicone matrix contained in acartridge which gradually releases the calcium hypochlorite biocidalactive ingredient. The application of the system as material for thetaking of impressions, in particular dental impressions, is not at alldealt with in this patent application.

It was found that the antiseptics used within the mass of materials asdescribed in EP-A-0 361 301, in EP-A-0 493 186 and in FR-A-2 707 660 donot meet the specifications specific to the applications of elastomermaterials in the field of hygiene and health and, more particularly butwithout limitation, in the case of materials for taking impressions, inparticular dental impressions.

The specifications considered comprise, inter alia, the followingspecifications:

the material loaded with blocide should be compatible for contact withthe skin and the mucous membranes, in particular the buccal mucousmembranes: it should be nontoxic, nonallergenic and nonirritant at theapplicable doses;

the material should contain a sufficient content of biocide in order tobe able to develop at the surface the desired antiseptic activityregardless of the mechanism of action: contact activity and/or releaseof small quantities of active product;

the biocidal agent should not develop any inhibitory activity towardsthe crosslinking catalysts, in particular towards platinum catalysts inthe case of the polyaddition EVF or RTV system;

the presence of biocidal agent in the material should not interfere withand hamper the technical performance features of the elastomer material;in particular, “the crosslinkability”, the setting time, the rheologicalproperties before crosslinking, the mechanical properties aftercrosslinking, the dimensional stability and the thermal stability,should not be affected.

In such a technical context, one of the essential objectives of thepresent invention is to provide a silicone elastomer system withbiocidal properties and which can be used in particular for the takingof impressions, for example dental impressions, it being necessary forthe said system, as far as possible, to comply with the abovementionedspecifications.

Another essential objective of the invention is to provide a biocidalsilicone elastomer system, in particular of the EVF 2 or RTV 2 type,which is simple to obtain, is inexpensive, is effective from the pointof view of the antiseptic activity and which possesses excellentphysical and chemical properties during use.

Another essential objective of the invention is to provide a materialfor the taking of dental impressions in particular which satisfies thespecifications aimed at above for the system.

Another essential objective of the invention is to propose the use of abiocidal silicone elastomer system for the taking of impressions, inparticular dental impressions.

Another essential objective of the present invention is to provide aprocess for preparing the abovementioned system which is industrial andnot very costly.

To achieve these objectives, among others, the inventors have had themerit of bringing up-to-date quite surprisingly and unexpectedly andafter long and laborious research studies and experiments, a judiciouslyselected class of biocidal agents which are active chlorine promoters.

Hence it follows that the present invention relates to a siliconeelastomer system, which can be used in particular for takingimpressions, in particular dental impressions, having biocidalproperties and characterized in that it essentially comprises:

(I) at least one polyorganosiloxane (POS) composition which can becrosslinked or which is crosslinked in elastomer form, and whichoptionally comprises at least one crosslinking catalyst,

(II) and at least one biocidal agent chosen from active chlorineprecursors, preferably from N-chlorinated compounds and more preferablystill from N-chloramines;

excluding silicone-based materials, in particular for dentalimpressions, comprising a hydrophobic antiseptic agent incorporated intothe mass of the silicone and capable of being gradually released as faras the surface of the impression material, this antiseptic agentconsisting in particular of ethylenediaminetetraacetic acid,benzalkonium chloride and sodium tosylchloramide or one of itsanalogues; and with the condition according to which in the case wherethe composition (I) comprises α,ω-di(hydroxy) POSs which can becrosslinked by polycondensation, then the concentration C_(II) ofbiocidal agent, expressed in % by weight relative to the total mass(I+II), is:

C_(II)<1

preferably C_(II)≦0.8

and more preferably still 0.001≦C_(II)≦0.5.

Considered as “biocides” for the purposes of the invention are theagents endowed with destructive properties towards live microorganismsof any type: bacteria, viruses, fungi, yeasts, in vegetative form(spores) or otherwise.

In addition to the advantageous selection of the biocidal agent fromactive chlorine precursors, the invention is also based on thequalitative and quantitative choice of the compatible siliconeelastomers. The synergistic combination of the POS composition I and ofthe biocidal agent II leads to a system or to a silicone elastomermaterial having the following advantages:

stably antiseptic over time,

endowed with all the advantageous properties of noncrosslinkedelastomers (fluidity, film-forming ability) and of crosslinkedelastomers (hardness, dimensional stability, thermal stability);

low production cost, in particular for making industrial moulds.

According to one characteristic of the invention, the POS composition(I) comprises POSs which can be crosslinked by polyaddition and moreoverthe concentration C_(II) of biocidal agent, expressed in % by weightrelative to the total mass (I+II), is:

C_(II)≦1

preferably C_(II)≦0.8

and more preferably still 0.001≦C_(II)≦0.5.

It is of particular interest to note that, at these low concentrations,the biocidal agent selected according to the invention is perfectlyeffective as regards the antiseptic activity, without as a resulthampering the reactivity of the polyaddition EVFs or RTVs forming thesilicone elastomer.

It is evident from the above that the POS composition (I) is preferablya polyaddition silicone composition which can be hardened to anelastomer by hydrosilylation reactions, characterized in that itcomprises:

(I_(a))—at least one diorganopolysiloxane oil having, per molecule, atleast two alkenyl, preferably vinyl, groups linked to the silicon;

(I_(b))—at least one diorganopolysiloxane oil having, per molecule, atleast three hydrogen atoms linked to the silicon,

(I_(c))—a catalytically effective quantity of a catalyst which is ingeneral a compound of a metal of the platinum group.

The quantities of (I_(a)) and (I_(b)) are generally chosen so that themolar ratio of the hydrogen atoms linked to the silicon in (I_(b)) tothe vinyl radicals linked to the silicon in (I_(a)) is generally between0.4 and 10, preferably between 0.6 and 5. This ratio however may bebetween 2 and 5 if it is desired to make elastomer foams.

The alkenyl groups in (I_(a)) and the hydrogen atoms in (I_(b)) aregenerally linked to different silicon atoms.

These compositions crosslink by addition reaction (also calledhydrosilylation reaction), catalysed by a compound of a metal of aplatinum group, of an alkenyl group of the organopolysiloxane (I_(a)) ona hydride function of the organopolysiloxane (I_(b)).

The alkenylated organopolysiloxane (I_(a)) may be an organopolysiloxanehaving siloxyl units of formula: $\begin{matrix}{Y_{a}Z_{b}{SiO}_{\frac{({4 - a - b})}{2}}} & (1)\end{matrix}$

in which Y is a vinyl group, Z is a monovalent hydrocarbon group whichdoes not have an unfavourable action on the activity of the catalyst, Zis generally chosen from alkyl groups having from 1 to 8 carbon atomsinclusive such as methyl, ethyl, propyl and 3,3,3-trifluoropropy groupsand aryl groups such as xylyl, tolyl and phenyl, a is 1 or 2, b is 0, 1or 2 and a+b is between 1 and 3, optionally all the other units beingunits having the average formula: $\begin{matrix}{Z_{c}{SiO}_{\frac{({4 - c})}{2}}} & (2)\end{matrix}$

in which Z has the same meaning as above and c has a value between 0 and3.

The organopolysiloxane I_(b) may be an organohydrogenopolysiloxanecomprising siloxyl units of formula: $\begin{matrix}{H_{d}W_{e}{SiO}_{\frac{({4 - d - e})}{2}}} & (3)\end{matrix}$

in which W is a monovalent hydrocarbon group having no unfavourableaction on the activity of the catalyst and having the same definition asZ, d is 1 or 2, e is 0, 1 or 2, d+e has a value between 1 and 3,optionally all the other units being units having the average formula:$\begin{matrix}{W_{g}{SiO}_{\frac{({4 - g})}{2}}} & (4)\end{matrix}$

in which W has the same meaning as above, g has a value between 0 and 3.

All the limiting values of a, b, c, d and g are included.

The organopolysiloxane (I_(a)) may consist solely of units of formula(1) and may contain, in addition, units of formula (2).

The organopolysiloxane (A) may have a linear branched cyclic or latticestructure. The degree of polymerization is 2 or more and is generallyless than 5 000. Moreover, if the organopolysiloxane (I_(a)) is linear,it has a viscosity at 25° C. of less than 500 000 mPa·s.

Z Is generally chosen from methyl, ethyl and phenyl radicals, at least60 mol % of the Z radicals being methyl radicals.

The organopolysiloxanes (I_(a)) and (I_(b)) are well known and are forexample described in patents U.S. Pat. No. 3,220,972, U.S. Pat. No.3,284,406, U.S. Pat. No. 3,436,366, U.S. Pat. No. 3,697,473 and U.S.Pat. No. 4,340,709.

Examples of siloxyl units of formula (1) are the vinyldimethylsiloxylunit, the vinylphenylmethylsiloxyl unit, the vinylsiloxyl unit and thevinylmethylsiloxyl unit.

Examples of siloxyl units of formula (2) are SiO_(4/2) dimethylsiloxane,methylphenylsiloxane, diphenylsiloxane, methylsiloxane andphenylsiloxane units.

Examples of organopolysiloxane (I_(a)) are dimethylpolysiloxanes withdimethylvinylsiloxyl ends, methylvinyldimethylpolysiloxane copolymerswith trimethylsiloxyl ends, methylvinyldimethylpolysiloxane copolymerswith dimethylvinylsiloxyl ends, cyclic methylvinylpolysiloxanes.

The organopolysiloxane (I_(b)) may consist solely of units of formula(3) or may comprise in addition units of formula (4).

The organopolysiloxane (I_(b)) may have a linear or branched, cyclic orlattice structure. The degree of polymerization is 2 between and 5 000.

The group W has the same meaning as the group Z above.

Examples units of formula (3) are:

H(CH₃)₂SiO_(1/2), HCH₃SiO_(2/2), H(C₆H₅)SiO_(2/2)

The examples of units of formula (4) are the same as those given abovefor the units of formula (2).

Examples of organopolysiloxane (I_(b)) are dimethylpolysiloxanes withhydrogenodimethylsilyl ends, dimethylhydrogenopolysiloxane copolymerswith trimethylsiloxyl ends, dimethylhydrogenomethylpolysiloxanecopolymers with hydrogenodimethylsiloxyl ends,hydrogenomethylpolysiloxanes with trimethylsiloxyl ends, cyclicmethylvinylpolysiloxanes.

The organopolysiloxane (I_(a)) and/or the organopolysiloxane (I_(b)) maybe diluted in a nontoxic organic solvent compatible with silicones.

The organopolysiloxanes (I_(a)) and (I_(b)) in the form of a lattice arecommonly called silicone resins.

The bases of polyaddition silicone compositions may comprise only linearorganopolysiloxanes (1) and (2) such as for example those described inthe abovementioned American patents: U.S. Pat. No. 3,220,972, U.S. Pat.No. 3,697,473 and U.S. Pat. No. 4,340,709, or may comprise both branchedand lattice organopolysiloxanes (I_(a)) and (I_(b)) such as for examplethose described in the abovementioned American patents: U.S. Pat. No.3,284,406 and U.S. Pat. No. 3,436,366.

The polyaddition composition may comprise, in addition, from 5 to 40parts by weight of polydimethylsiloxane oil(s) blocked at each of thechain ends by a (CH₃)₃SiO_(0.5) unit, having a viscosity at 25° C. ofbetween 10 and 5 000 mPa·s per 100 parts of organopolysiloxanes (I_(a))and (I_(b))

The catalysts (I_(c)) are also well known. The compounds of platinum andrhodium are preferably used. It is possible to use the complexes ofplatinum and of an organic product described in American patents U.S.Pat. No. 3,195,601, U.S. Pat. No. 3,159,602, U.S. Pat. No. 3,220,972 andEuropean patents EP-A-57 459, EP-A-188 978 and EP-A-190 530, thecomplexes of platinum and of vinylated organopolysiloxane which aredescribed in American patents U.S. Pat. No. 3,419,593, U.S. Pat. No.3,715,334, U.S. Pat. No. 3,377,432 and U.S. Pat. No. 3,814,730.

It is also possible to use the complexes of rhodium which are describedin British patents: GB-A-1 421 136 and GB-A-1 419 769.

The platinum catalysts are preferred. In this case, the quantity byweight of catalyst (I_(c)) calculated by weight of platinum metal isgenerally between 2 and 600 ppm, in general between 5 and 200 ppm basedon the total weight of the organosiloxanes (I_(a)) and (I_(b)).

The polyaddition compositions preferred in the context of the presentinvention are those which comprise:

(I_(a)): at least one diorganopolysiloxane oil blocked at each end ofits chain with a vinyldiorganosiloxyl unit whose organic radicals linkedto the silicon atoms are chosen from methyl, ethyl and phenyl radicals,at least 60 mol % of these radicals being methyl radicals, having aviscosity of 100 to 500 000, preferably of 1 000 to 200 000 mPa·s at 25°C.;

(I_(b)): at least one organohydrogenopolysiloxane chosen from the linearor lattice liquid copolymers and homopolymers having per molecule atleast 3 hydrogen atoms linked to different silicon atoms and in whichthe organic radicals linked to the silicon atoms are chosen from methyland ethyl radicals and at least 60% of these radicals being methylradicals, the product (I_(b)) being used in a quantity such that themolar ratio of the hydride functions to the vinyl groups is between 1.1and 4:

(I_(c)): a catalytically effective quantity of a platinum catalyst.

More preferably still, up to 50% by weight of the polymer I_(a) isreplaced by a lattice copolymer comprising trimethylsiloxyl,methylvinylsiloxyl and SiO_(4/2) units in which 2.5 to 10 mol % of thesilicon atoms comprise a vinyl group and in which the molar ratio of thetrimethylsiloxyl groups to the SiO_(4/2) group is between 0.5 and 1.

According to a variant and provided that C_(II) is less than 1% byweight, the POS composition (I) is a diorganopolysiloxane compositionwhich can be hardened to a silicone elastomer by polycondensationreactions comprising:

(I_(a′)): at least one diorganopolysiloxane oil carrying at each end ofthe chain at least two condensable or hydrolysable groups, or a singlehydroxyl group,

(I_(b′)): a silane comprising at least three condensable or hydrolysablegroups, and/or a product obtained from the partial hydrolysis of thissilane, when (A) is an oil with hydroxyl ends,

(I_(c′)): a polycondensation catalyst.

The diorganopolysiloxane oils (I_(a′)) which can be used in thecompositions according to the invention are more particularly thosecorresponding to the formula (1′):

Y_(n)Si_(3−n)O(SiR₂O)_(x)SiR_(3−n)Y_(n)  (1′)

in which:

R represents identical or different monovalent hydrocarbon radicals andY represents identical or different hydrolysable or condensable groups,or hydroxyl groups,

n is chosen from 1, 2 and 3 with n=1, when Y is a hydroxyl, and x is aninteger greater than 1, preferably greater than 10.

The viscosity of the oils of formula (1′) is between 50 and 10⁶ mPa·s at25° C. As examples of R radicals, there may be mentioned alkyl radicalshaving from 1 to 8 carbon atoms such as methyl, ethyl, propyl, butyl,hexyl and octyl, vinyl radicals, phenyl radicals.

As examples of substituted R radicals, there may be mentioned3,3,3-trifluoropropyl, chlorophenyl and beta-cyanoethyl radicals.

In the products of formula (1′) which are generally used industrially,at least 60% in numerical terms of the R radicals used are methylradicals, the other radicals being generally phenyl and/or vinylradicals.

As examples of hydrolysable Y groups, there may be mentioned amino,acylamino, cetiminoxy, iminoxy, enoxy, alkoxy, alkoxyalkyleneoxy,acyloxy and phosphate groups and, for example, among these:

for the Y amino groups: n-butylamino, sec-t-butylamino andcyclohexylamino groups

for the N-substituted acylamino groups: the benzoylamino group,

for the aminoxy groups: the dimethylaminoxy, diethylaminoxy,dioctylaminoxy and diphenylaminoxy groups,

for the iminoxy and citiminoxy groups: those derived from acetophenoneoxime, acetone oxime, benzophenone oxime, methylethyl ketoxime,diisopropyl ketoxime and chlorocyclohexanone oxime,

for the Y alkoxy groups: the groups having from 1 to 8 carbon atoms suchas the methoxy, propoxy, isopropoxy, butoxy, hexyloxy and octyloxygroups,

for the Y alkoxyalkyleneoxy groups: the methoxyethyleneoxy group.

for the Y acyloxy groups: the groups having from 1 to 8 carbon atomssuch as the formyloxy, acetoxy, propionyloxy and 2-ethylhexanoyloxygroups,

for the Y phosphate groups: those which are derived from dimethylphosphate, diethyl phosphate and dibutyl phosphate groups.

As condensable v groups, there may be mentioned hydrogen atoms andhalogen atoms, preferably chlorine.

When in the Formula (1′) above the Y groups are hydroxyl groups, n isthen equal to 1, it is necessary, in order to prepare polyorganosiloxaneelastomers from polymers of formula (1′) above, to use, in addition tocondensation catalysts, crosslinking agents (I_(b′)) which are silanesof general formula:

R_(4−a)SiY′_(a)  (2′)

in which:

R has the meanings given above in formula (1′) and Y′ representshydrolysable or condensable groups, which are identical or different, ais equal to 3 or 4.

The examples given for the Y groups are applicable to the Y′ groups.

It is desirable to use silanes of formula (2′) in the same case wherethe oil (A) Y is not a hydroxyl group. It is then preferable to use Ygroups of the oil (I_(a)) which are identical to the Y′ groups of thesilane (I_(b′))

The α,ω-dihydroxylated diorganopolysiloxanes of formula (1′) aregenerally oils whose viscosity varies from 500 mPa·s at 25° C. to 500000 mPa·s at 25° C., preferably 800 to 400 000 mPa·s at 25° C., they arelinear polymers essentially consisting of diorganosiloxyl units offormula (R₂SiO).

However, the presence of other units, generally at impurities, such asRSiO_(3/2), RSiO_(1/2) and SiO_(4/2), is not excluded in the proportionin particular of at most 1% relative to the number of diorganosiloxylunits.

The organic radicals, linked to the silicon atoms of the parent oils,represented by the symbol R, may be chosen from the alkyl radicalshaving from 1 to 3 carbon atoms such as the methyl, ethyl and n-propylradicals, the vinyl radical, the phenyl radical, the3,3,3-trifluoropropyl radical and the beta-cyanoethyl radical.

Preferably, at least 60% of the whole of the R radicals are methylradicals, at most 1% are vinyl radicals.

By way of illustration of units represented by the formula R₂SiO, theremay be mentioned those of formulae:

(CH₃)₂SiO; CH₃(CH₂=CH)SiO; CH₃(C₆H₅)SiO;

CF₃CH₂CH₂(CH₃)SiO; NC—CH₂CH₂(CH₃)SiO; NC—CH₂(C₆H₅)SiO;

These parent oils are, for the most part, marketed by manufacturers ofsilicones. Moreover, their manufacturing techniques are well known: theyare described for example in French patents FR-A-1 134 005, FR-A-1 198749, FR-A-1 226 745.

As examples of monomeric silanes (I_(b′)) of formula (2′), there may bementioned more particularly polyacyloxysilanes, polyalkoxysilanes,polycetiminoxysilanes and polyiminoxysilanes and in particular thefollowing silanes:

CH₃Si(OCOCH₃)₃; C₂H₅Si(OCOCH₃)₃;

(CH₂═CH)Si(OCOCH₃)₃; C₆H₅Si(OCOCH₃)₃;

CF₃CH₂CH₂Si(OCOCH₃)₃;

NC—CH₂CH₂Si(OCOH₃)₃; CH₂ISi(OCOH₂CH₃)₃;

CH₃Si(ON═C(CH₃)C₂H₅)₂OCH₂CH₂OCH₃;

CH₃Si(ON═CH—CH₃)₂OCH₂CH₂OCH₃

The above (I_(b′)) silanes associated with alpha-omega-dihydoxylatedpolydiorganosiloxanes of formula (1′) may be used in monocomponentcompositions which are stable when protected from air.

As examples of monomeric silane of formula (2′) which, combined withalpha-omega-dihydroxylated polydiorganosiloxanes of formula (1′), may beadvantageously used in bicomponent compositions, there may be mentionedthe polyalkoxysilanes and in particular those of formulae:

 Si(OC₂H₅)₄; Si(O-n-C₃H₇)₄; Si(OC₂H₄OCH₃)₄;

CH₃Si(OCH₃)₃; CH₂═CHSi(OCH₃)₃; CH₃Si(OC₂H₄OCH₃)₃;

CICH₂Si(OC₂H₅)₃; CH₂═CHSi(OC₂H₄OCH₃)₃

All or some of the monomeric silanes described above may be replaced bypolyalkoxysilanes in which each molecule comprises at least two,preferably three Y′ atoms, the other valencies of the silicon aresatisfied by siloxane bonds SiO and SiR.

As examples of polymeric cross inking agents, ethyl polysilicate may bementioned.

0.1 to 20 parts by weight of crosslinking agent of formula (2′) aregenerally used per 100 parts by weight of polymer of formula (1′).

The polyorganosiloxane compositions which can be hardened to anelastomer of the type described above comprise from 0.001 to 10 parts byweight, preferably from 0.005 to 3 parts by weight of condensationcatalyst (I_(c′)) per 100 parts by weight of polysiloxane of formula(1).

The content of condensation catalyst for the monocomponent compositionsis generally much smaller than that used in the bicomponent compositionsand is generally between 0.001 and 0.05 parts by weight per 100 parts byweight of polysiloxane of formula (2′).

The crosslinking agents (I_(b′)) of formula (2′), whether they can beused for the preparation of monocomponent or bicomponent compositions,are products which are accessible on the market for silicones;furthermore, their use in compositions which harden from roomtemperature upwards is known; it appears in particular in French patentsFR-A-1 126 411, FR-A-1 179 969, FR-A-1 189 216, FR-A-1 198 749, FR-A-1248 826, FR-A-1 314 649, FR-A-1 423 477, FR-A-1 432 799 and FR-A-2 067636.

According to an advantageous feature of the invention, the POScomposition (I), whether it is of the polyaddition type or of thepolycondensation type, comprises in addition one or more functionaladditives (I_(d)) chosen from the group comprising:

inhibitors of the polyaddition crosslinking reaction, preferablyplatinum catalyst inhibitors;

reinforcing and/or semireinforcing and/or bulking fillers,

plasticizing agents,

and mixtures thereof.

The inhibitors are well-known compounds. There may be used in particularorganic amines, silazanes, organic oximes, dicarboxylic acid diesters,acetylenic alcohols, acetylenic ketones, vinylmethylcyclopolysiloxanes(see for example U.S. Pat. No. 3,445,420 and U.S. Pat. No. 3,989,667).The inhibitor is used In an amount of form 0.005 to 5 parts by weight,preferably from 0.01 to 3 parts by weight to 100 parts of theconstituent (I_(a)).

The reinforcing or semireinforcing or bulking fillers are preferablychosen from siliceous fillers.

The reinforcing siliceous fillers are preferably chosen from fumedsilicas and precipitated silicas. They have a specific surface area,measured according to the BET methods, of at least 50 m²/g, preferablygreater than 70 m²/g, a mean primary particle size of less than 0.1 μm(micrometre) and an apparent density of less than 200 g/liter.

These silicas may be incorporated as they are or after having beentreated with organosilicon compounds normally used for this use. Amongthese compounds are methylpolysiloxanes such as hexamethyldisiloxane,octamethyldisiloxane, octamethylcyclotetrasiloxane, methylpolysilazanessuch as hexamethyldisilazane, hexamethylcyclotrisilazane, chlorosilanessuch as dimethylchlcrcsilane, trimethylchlorosilane,methylvinyldichlorosilane, dimethylvinylchlorosilane, alkoxysilanes suchas dimethyldimethoxysilane, dimethylvinylethoxysilane,trimethylmethoxysilane.

During this treatment, the silicas may increase their starting weight upto a level of 20%, preferably 18% approximately.

The semireinforcing or bulking fillers have a particle diameter greaterthan 0.1 μm and are preferably chosen from ground quartz, calcinedclays, diatomaceous earth and aluminium silicates and/or sodiumsilicates.

The semireinforcing or bulking fillers may also consist of fillers basedon alumina and titanium oxide.

From the weight point of view, the fillers may represent from 5 to 100parts by weight, preferably from 5 to 50 parts by weight per 100 partsof the sum of the POSs I_(a) or (I_(a′))+I_(b) or (I_(b′))

The plasticizing agents capable of constituting additional additives(_(d)) may be for example liquid paraffin and/or a paraffin.

The POS compositions (I) more especially envisaged in the context of theinvention are compositions with two components or with two packagings,also called bicomponent compositions A-B. They are precursors of theelastomers crosslinked at room temperature or by heat in order toaccelerate the reaction. This crosslinkage is obtained by mixingcomponents A and B, which are not hardenable separately.

In the case of the preferred polyaddition POS compositions (I), it isdesirable that they comprise a crosslinking inhibitor as long as theyare in the form of bicomponent compositions in two packagings. Indeed,the inhibition provides a delay which makes it possible to obtain goodhomogenization of the mixture constituting the EVF 2 or RTV 2//biocidesystem according to the invention.

To obtain good homogenization of distribution of the active substance,it is indeed desirable for the silicone matrix to have a degree ofviscosity of the order of 5 000 to 30 000 mPa·s at 25° C.

Such a viscosity may be obtained by precrosslinking, the latter beingblocked at the desired viscosity by addition of an inhibitor. Sufficienttime is thus available in order to properly homogenize the activesubstance inside the silicone matrix.

The crosslinking is then achieved by heating the matrix to a temperaturesuch that the inhibitor no longer has any effect on the catalytic actionof platinum.

As regards the biocidal agent (II) used in the system according to theinvention, it should be noted that it is preferably chosen from theactive chlorine precursor group based on n-chlorinated compoundscomprising:

chloramine B (sodium N-chlorobenzenesulphonamide),

chloramine T (sodium N-chloro-p-toluenesulphonamide),

dichloramine T (N,N-dichloro-p-toluenesulphonamide),

N-trichloromethylmercapto-4-cyclohexene-1,2-dicarboxylamide),

halazone (p-n-dichlorosulphonamidebenzoic acid)

N-chlorosuccinide

trichloromelamine

N-chloro derivatives of cyanuric acids, preferably trichloroisocyanuricacid and/or sodium dichloroisocyanuric dihydrate,

N-chlorohydantoins, preferably 1-bromo-3-chloro-5,5′-dimethylhydantoin,or 1,3-dichloro-5,5′idimethylhydantoin,

and mixtures thereof.

This group of antiseptics essentially corresponds to the N-chloraminefamily which comprises derivatives of amines in which one or two of thevalencies of the trivalent nitrogen are substituted by chlorine. In thepresence of water, the N-chloramines produce hypochlorous acid HClO orsalts of this acid such as NaClO. HClO is NaClO are active chlorinatedderivatives endowed with a high bactericidal capacity, which isexploited in the context of the system according to the invention.

According to an advantageous characteristic of the invention, the systemto which it relates is obtained by mixing the POS composition (I) withthe biocidal agent in the form of a suspension or a solution, preferablyalcoholic.

Advantageously, the biocidal agent (II) is combined with at least oneantiseptic auxiliary agent (III) different from the antiseptics whichwork by releasing chlorine and preferably chosen from the group ofsurfactant formulations comprising one or more quaternary ammoniums andoptionally at least one sequestering activator, preferably selected frommetal ion complexing agents.

According to another mode of defining the biocidal agent (II), it may bespecified that the latter is advantageously free of inhibitory activityon the crosslinking of the PCS composition (I).

In practice, the system according to the invention may be, for example,such that:

the POS composition (I) comprises:

(I_(a)): at least one diorganopolysiloxane oil blocked at each end ofits chain by a vinyldiorganosiloxyl unit in which the organic radicalslinked to the silicon atoms are chosen from methyl, ethyl and phenylradicals, at least 60 mol % of these radicals being methyl radicals,having a viscosity of 100 to 500 000, preferably of 1 000 to 200 000mPa·s at 25° C.;

(I_(b)): at least one organohydrogenopolysiloxane chosen from the linearor lattice liquid copolymers and homopolymers having per molecule atleast three hydrogen atoms linked to different silicon atoms and inwhich the organic radicals linked to the silicon atoms are chosen frommethyl and ethyl radicals and at least 60% of these radicals beingmethyl radicals, the product (I_(b)) being used In a quantity such thatthe molar ratio of the hydride functions to the vinyl groups is between1.1 and 4:

(I_(c)): a catalytically effective quantity of a platinum catalyst.

(I_(d)): one or more functional additives preferably chosen from thegroup comprising silicas, aluminas, silicates, vinyl disiloxanes, liquidparaffins, paraffins and mixtures thereof.

the biocidal agent (II) comprises a chloramine, preferably sodiumtosylchioramide or one of its chlorinated analogues,

the biocidal agent (II) is optionally combined with an antisepticauxiliary agent (III), preferably benzalkonium chloride, advantageouslysupplemented with an activator-sequestrant, preferably EDTA.

According to another of its aspects, the invention also relates to amaterial for taking impressions, in particular dental impressions,comprising a system as defined above.

Advantageously, this material comprises, in addition, adjuvants selectedfrom sweeteners, preferably synthetic sweeteners, and/or fromflavourings, and/or from colourings and/or from anti-inflammatoryagents, and/or from isotanic products, preferably saccharides, morepreferably still hydrogenated saccharides, sorbitol being mostespecially selected, and mixtures thereof.

By way of example of synthetic sweeteners, there may be mentioned theproducts marketed under the trade marks ASPARTAM®, ACESULFAM®, and thelike.

Mint flavour is among the flavours which can be used.

As an example of an anti-inflammatory adjuvant, allantoin or one of itsanalogues may be mentioned.

Benzalkonium chloride or one of its analogues is a commerciallyavailable surfactant and antiseptic quaternary ammonium.

The biocidal agent (II) used in the context of the invention may be forexample a formulation comprising an active chlorine precursor such as achloramine as well as antiseptic auxiliary agents (III), a sequesteringactivator and adjuvants. Calbenium having the following composition isan example of these formulations:

EDTA (ethylenediamine- 100 ± 50 parts by weight tetraacetic acid) or oneof its analogues Sodium tosylchloramide or 2 ± 1 part by weight one ofits analogues Benzalkonium chloride or 12 ± 6 parts by weight one of itsanalogues Aspartame or any synthetic 8 ± 4 parts by weight orsemisynthetic sweetener Mint or any flavouring 10 ± 5 parts by weightAllantoin or one of its 6 ± 3 parts by weight analogues Sorbitol or oneof its 132 ± 66 parts by weight analogues

formulation for a dose of 2.5 g necessary for one liter of water.

The present invention also relates to a process for preparing the systemor the material as described above. This process is characterized inthat it essentially consists in mixing the POS compounds (I), thebiocidal agent (II) and optionally the antiseptic auxiliary agent (III)advantageously supplemented with the activator-sequestrant, andoptionally the adjuvants as mentioned above.

This mixing is traditionally carried out by appropriate technical meansknown to persons skilled in the art.

According to an advantageous proposition mentioned above, it ispreferable to introduce the biocidal agent II in the form of analcoholic solution.

The subject of the present invention is also the use of the system ormaterial, as described above, for taking dental impressions, this usebeing characterized in that it essentially consists in ensuring that thecrosslinking of the silicone elastomer is preferably initiated by mixingcomponents A and B, in taking the dental impression and in allowing thecrosslinking to continue until the elastomer is sufficiently crosslinkedor is sufficiently hard.

The invention will be more clearly understood with the aid of thefollowing examples which describe the preparation of the biocidalsilicone elastomer system according to the invention as well as itsevaluation in terms of mechanical properties and antiseptic properties.

EXAMPLES Examples 1 to 3 and Trials 1 to 3

I—In Examples 1 to 3, the crosslinking bicomponents are prepared bypolyaddition reactions, leading to the first impression pasty products(so-called type I bicomponents).

1. List of the Raw Materials Used

1.1. - Part A of the bicomponent: POS (I_(a)): Polydimethylsiloxane oilblocked at each of the ends of the chains by a unit (CH³)₂ ViSiO_(0.5)of viscosity 100 000 mPa.s and containing about 0.0024 vinyl (Vi)function in 100 g of oil that is about 0.065% by weight of Vi function;POS (I_(a1)): Oil of the same nature as POS (I_(a)) but having aviscosity of 600 mPa.s, containing about 0.014 Vi function in 100 g ofoil, that is about 0.38% by weight of Vi function; POS (1_(a2)):retarder of the polyaddition reaction consisting ofdivinyltetramethyldisiloxane; Functional additives (I_(d)) Filler 1:aluminium silicate and sodium silicate, marketed under the name SIPERNAT44; Filler 2: hydrate of alumina, marketed under the name ALLUMINA M15/B; Filler 3: siliceous material based on diatomaceous earth, marketedunder the name DICALITE WHITE FILLER; Ingredient 1: liquid paraffin;Ingredient 2: paraffin, marketed under the name PARAFFINE RAFF. LASTRE52/5; Catalyst (I_(c)): platinum zero complexed withdivinyltetramethyldisiloxane: there is used a solution in divinyltetra-methyldisiloxane of a complex of platinum containing about 11% by weightof platinum zero in the form of a ligand withdivinyltetramethyldisiloxane; the quantities of this catalyst areexpressed as parts by weight of solution used. 1.2. - Part B of thebicomponent: POS (I_(a)): cf. part A; POS (I_(a1)): cf. part A; POS(I_(b)): poly(dimethyl) (methylvinyl)siloxane gum blocked at each of theends of the chains by a unit (CH₃)₂ViSiO_(0.5) having a weight-averagemolecular mass of 540 000 g/mol, containing about 0.00185 Vi function in100 g of gum, that is about 0.05% by weight of Vi function; POS(1_(b1)): poly(dimethyl) (hydrogenomethyl)- siloxane oil blocked at eachof the ends of the chains by a unit (CH₃)₂HiSiO_(0.5), having aviscosity of 30 mPa.s and containing about 0.25 H function in 100 g ofoil, that is about 0.25% by weight of H; Functional additives (I_(d))Filler 1: cf. part A; Filler 2: cf. part A; Filler 3: cf. part A;Ingredient 1: cf. part A; Ingredient 2: cf. part A; Bactericide (II):solution containing 80% by weight of calbenium (80 parts) in ethylalcohol at 96% (20 parts).

2. Constitution of Parts A and B of Bicomponents I Tested

Part A Part B POS (I_(a)) 14.45* 11.4 POS II (I_(a1)) 7.40 4.6 POS III(1_(a2)) 0.035 — POS IV (I_(b)) — 4.8 POS V (I_(b1)) — 2.45 Functionaladditives (I_(d)) Filler 1 40.0 31.2 Filler 2 21.0 29.6 Filler 3 10.08.25 Ingredient 1 6.5 7.0 Ingredient 2 0.6 0.7 Catalyst (I_(c)) 0.015 —Bactericide (II) — Ex. 1 Ex. 2 Ex. 3 0.25 0.75 1.25 (*: parts by weight)

3. Preparation of the Compositions

3.1—Part A:

(1) The following constituents are introduced, at 23° C., into aplanetary mixer: PCS (I_(a)), POS (I_(a1)), filler 1 and filler 2; thewhole is homogenized by stirring at 20 revolutions/min for 1 hour.

(2) The stirring is then stopped and the filler 3 is then added: anotherhomogenization at revolutions/min for 1 hour.

(3) The stirring is then stopped and the ingredients 1 and 2 are thenadded: another homogenization at 20 revolutions/min for 1 hour.

(4) The stirring is then stopped and the catalyst and the POS (I_(a2))are then added: another homogenization at 20 revolutions/min for 30minutes.

(5) Then, without stopping the stirring, the mass is degassed by workingat 23° C., under a reduced pressure of 226×10² Pa, for 20 minutes.

3.2—Part B:

The following steps are carried out in the preceding mixer:

(1) Introduction of the POS (I_(a)), POS (I_(a1)), POS (I_(b)) filler 1and filler 2 and homogenization at 23° C., with stirring of 20 rev/min,for 1 hour;

(2) Stoppage of stirring and addition of the filler 3: homogenizationfor 3 hours at 20 rev/min;

(3) Stoppage of stirring and addition of the ingredients 1 and 2:homogenization for 1 hour at 20 rev/min;

(4) Stoppage of stirring and addition of the bactericide in the desiredquantity and of POS (I_(b1)): homogenization for 30 minutes at 20rev/min;

(5) Degassing as indicated above for part A;

3.3. Bicomponents A+B of type I:

The dental RTV composition is obtained by mixing, at room temperature(23° C.), 50 parts by weight of part A and 50 parts by weight of part B.The crosslinking of each bicomponent composition is carried out at roomtemperature after preparing the mixture.

II—Comparative trials (trials 1 to 3) were carried out usingbicomponents of a similar nature, but in which the bactericide consistsof benzalkonium chloride (so-called type II bicomponents).

1. List of the Raw Materials Used

1.1. Part A:

POS (I_(a)), POS (I_(a1)), PCS (I_(a2)) and filler 1: cf. part A, in§I.1.1;

Filler 2: hydrate of alumina, marketed under the name ALLUMINE ALCOA M10;

Filler 3: siliceous material based on diatomaceous earth, marketed underthe name CELITE SUPER FLOS;

Ingredients 1 and 2 and catalyst: cf. part A, in §I-1.1.

1.2. Part B:

POS (I_(a)), POS (I_(a1)), POS (I_(b)), POS (I_(b1)) and filler 1: cf.part B, in §I-1.2.;

Fillers 2 and 3: cf. part A,; in §II-1.1.;

Ingredients 1 and 2: cf. part B,; in §I-1.2.;

Bactericide (II): solution containing 50% by weight of benzalkoniumchloride (50 parts) in ethyl alcohol at 96% (50 parts)

2. Constitution of Parts A and B of the Bicomponents II Tested

Part A Part B POS (I_(a)) 14.45* 11.3 POS (I_(a1)) 7.40 4.0 POS (I_(a2))0.035 — POS (I_(b)) — 4.8 POS (I_(b1)) — 3.1 Functional additives(I_(d)) Filler 1 40.0 30.8 Filler 2 21.0 28.8 Filler 3 10.0 8.9Ingredient 1 6.5 7.0 Ingredient 2 0.6 0.7 Catalyst (I_(c)) 0.015 —Bactericide (II) — Trial 1 Trial 2 Trial 3 0.5 1.0 2.0 (*: parts byweight)

3. Preparation of the Compositions

3.1—Part A:

The procedure is carried out as above in §I-3.1.

3.2—Part B:

The procedure is carried out as indicated above in §I-3.2., but with thefollowing slight modifications:

step (1) to (5): stirring at 50 revolutions/min; step (3): addition ofingredients 1 and 2 and of the bactericide; step (4): addition of thesole POS V and homogenization for 1 hour.

3.3. Bicomponents A+B of type II:

The crosslinking of the bicomponent is carried out, as indicated abovein §I-3.3., at room temperature after mixing the 2 parts A and B in a50/50 ratio by weight.

III—Results

They are assembled in Table 1 below. This table indicates the contentsof bactericidal agent which were introduced according to the techniquedescribed above, as well as the working time and the setting time forthe products obtained. The working time corresponds to the time duringwhich the mixture of the 2 parts A and B retains a fluid behaviour;beyond, the material acquires the characteristics of an elastomer. Thesetting time corresponds to the time necessary for the dental impressionto become capable of being handled.

TABLE I Ex. 1 Ex. 2 Ex. 3 Trial 1 Trial 2 Trial 3 Bicomponent type I I III II II Bactericide nature: calbenium calbenium calbenium benzalkoniumbenzalkonium benzalkonium chloride chloride chloride % by weight in A +b 0.1 0.3 0.5 0.125 0.25 0.5 Initial properties measured afterpreparation of parts A and B and mixtures thereof: working time: 1 min50 s 1 min 50 s 2 min 2 min 2 min 15 s 2 min 30 s setting time 2 min 20s 2 min 30 s 2 min 50 s 5 min 6 min 6 min 30 s Properties measured afterx = 180 x = 180 x = 180 x = 30 storing parts A and B separated x days at23° C.: working time: 2 min 2 min 50 s 2 min 10 s — setting time: 2 min30 s 2 min 50 s 3 min >10 min

Examples 4 to 6 and Trials 4 to 6

I—In Examples 4 to 6, bicomponents crosslinking by polyadditionreactions are prepared, leading to second impression fluid products(so-called type III bicomponents).

1. List of the Raw Materials Used

1.1. Part A: POS (I_(a)) and (Ia₁): cf. part A, Examples 1-3, § I-1.1.;Functional additives (I_(d)) Filler 4: fumed silica, marketed under thename AEROSIL 200, treated with hexamethyldisilazane; Filler 5: groundquartz having a mean particle diameter of 10 μm, marketed under the nameSICRON SA 600; Filler 6: TiO₂; Ingredient 3: polyoxyethylated andpropylated C₈-C₁₀ fatty alcohol, marketed under the name SOPROFOR BO327; Catalyst (I_(c)): cf. part A, Examples 1-3, § I-1.1. 1.2. - Part B:POS (I_(a)) and (I_(a1)): cf. part A, immediately above; POS (I_(b1)):cf. part B, Example 1-3, § I-1.2.; Functional additives (I_(d)) Fillers4, 5 and 6: cf. part A, immediately above; Ingredient 3: cf. part A,immediately above; Bactericide: solution containing 80% by weight ofcalbenium (80 parts) in ethyl alcohol at 96% (20 parts).

2. Constitution of Parts A and B of the Bicomponents III tested

Part A Part B POS (I_(a)) 2.0* 6.0 POS (I_(a1)) 52.0 42.3 POS (I_(b1)) —8.0 Functional additives (I_(d)) Filler 4 12.0 12.0 Filler 5 34.5 35.0Filler 6 0.6 0.5 Ingredient 3 0.3 0.3 Catalyst (I_(c)) 0.01 —Bactericide (II) — Ex. 4 Ex. 5 Ex. 6 0.25 0.75 1.25 (*: parts by weight)

3. Preparation of the Compositions

3.1—Part A:

(1) In a first instance, a basic mixture (abbreviated BM) is prepared bymixing at room temperature (23° C.) 24 parts by weight of filler 4 and56 parts by weight of POS (II).

(2) For the preparation of part A, 40 parts of BM are mixed in a turbinedispersing device with POS I, the remainder of POS (II) (24 parts), thefillers 5 and 6 and the ingredient 3: the procedure is carried out at23° C., with stirring at 450 rev/min, for 2 hours.

(3) The stirring is then stopped and then it is checked that thetemperature of the mass is ≦70° C. before adding the catalyst:homogenization for 10 minutes at 450 rev/min, and then degassing of themass, the procedure being carried out under a reduced pressure of266×10² Pa for 10 minutes.

3.2—Part B:

(1) 40 parts of the remaining BM are mixed with the POS (I_(a)), theremainder of POS (I_(a)), the remainder of POS (I_(a1)) (14.3 parts),the fillers 5 and 6 and the ingredient 3: next, homogenization for 1hour at 450 rev/min.

(2) he stirring is then stopped and POS (I_(b1)) is then added: thehomogenization is then resumed for 10 minutes at 450 rev/min.

(3) Another stopping of the stirring and, after having checked that thetemperature of the mass is ≦70° C., the bactericide is added: next,homogenization for 10 minutes at 450 rev/min; then degassing asindicated above, at the end of part A.

3.3. Bicomponents A+B of type III:

The crosslinking of the bicomponents is carried out, here again, at roomtemperature (23° C.) after mixing the 2 parts A and B in a 50/50 ratioby weight. II—Comparative trials (trials 4 to 6) were carried out usingbicomponents of a similar nature, but in which the bactericide consistsof benzalkonium chloride (so-called type IV bicomponents).

1. List of the Raw Materials Used

1.1. Part A: POS (I_(a)) and (I_(a1)): cf. part A, Examples 4-6, §I-1.1.; POS (I_(a2)): cf. part A, Examples 1-3, § I-1.1.; Functionaladditives (I_(d)) Fillers 4, 5 and 6: cf. part A, Examples 4-6, §I-1.1.; Filler 7: fumed silica, marketed under the name AEROSIL 200,treated with octamethylcyclotetrasiloxane; Ingredient 3 and cf. part A,catalyst (I_(c)): Examples 4-6, § I-1.1. 1.2. Part B: POS (I_(a)) and(I_(b2)) + cf. part B, Examples 4-6, § I-1.2.; fillers 4 and 5 +ingredient 3: Bactericide: solution containing 50% by weight ofbenzalkonium chloride (50 parts) in ethyl alcohol at 96% (50 parts)

2. Constitution of Parts A and B of the Bicomponents IV Tested

Part A Part B POS (I_(a)) 2.0 — POS (I_(a1)) 49.46 40.7 POS (I_(a2))0.03 — POS (I_(b2)) — 11.0 Functional additives (I_(d)) Filler 4 12.414.6 Filler 5 34.5 34.0 Filler 6 0.5 — Filler 7 1.0 — Ingredient 3 0.10.3 Catalyst (I_(c)) 0.01 — Bactericide (II) — Trial 5 Trial 6 Trial 70.5 1.0 2.0 (*: parts by weight)

3 Preparation of the Compositions

3.2—Part A:

The procedure is carried out as indicated above in §I-3.1. of Examples 4to 6, but with the following modifications:

step (1): the BM is prepared by mixing 27 parts by weight of filler 4and 63 parts by weight of POS (I_(a1));

step (2): 41.3 parts of the BM are mixed with the POS (I_(a)) theremainder of POS (I_(a1)) (20.55 parts), the fillers 5, 6 and 7 and theingredient 3;

step (3): the catalyst and the PCS (I_(a2)) are added.

3.2—Part B:

The procedure is carried out as indicated above in §I-3.2. of Examples 4to 6, but with the following modifications:

step (1): 48.7 parts of the rest of the BM are mixed with the remainderof POS (I_(a1)) (6.61 parts);

step (2): there are added thereto the filler 5 in place of POS (I_(b1))and the mixture is homogenized for 2 hours;

step (3): there are added, this time, apart from the bactericide, thePOS (I_(b1)) and the ingredient 3, and the mixture 5s homogenized for 1hour 30 minutes.

3.2. Bicomponents A+B of type IV:

The crosslinking of the bicomponents is carried out, here again, at roomtemperature (23° C.) after mixing the two parts A and B in a 50/50 ratioby weight.

III—Results

They are assembled in the following Table 2.

TABLE 2 Ex. 4 Ex. 5 Ex. 6 Trial 4 Trial 5 Trial 6 Bicomponent type IIIIII III IV IV IV Bactericide nature: calbenium calbenium calbeniumbenzalkonium benzalkonium benzalkonium chloride chloride chloride % byweight in A + B 0.1 0.3 0.5 0.125 0.25 0.5 Initial properties measuredafter preparation of parts A and B and mixtures thereof: working time: 2min 30 s 2 min 40 s 2 min 50 s 2 min 3 min  4 min setting time 5 min 10s 6 min 8 min 5 min 8 min >15 min Properties measured after x = 180 x =180 x = 180 x = 30 storing parts A and B separated x days at 23° C.:working time: 2 min 30 s 2 min 50 s 2 min 55 s — setting time: 5 min 20s 6 min 15 s 8 min 20 s >30 min

Example 7—Bactericidal Activity

The bactericidal activities of the systems according to Examples 1 to 6and according to trials 1 to 6 were evaluated in the following manner.

Films whose thickness is 2 mm and whose side is 2.5 cm are prepared bycrosslinking, at room temperature, an appropriate mixture of parts A andB of the systems tested.

The silicone squares are soaked in a bacterial suspension ofStaphylococcus aureus having a titre of 105 CFU/ml, so that themicroorganisms are in contact both with the edge and the surface of thesquares.

After a contact time of 30 min, the films are removed and kept underrelative humidity conditions (STP 50), this being up to the time ofplacing in culture, that is after 6 h, 24 h, 3 days and one week, and atlaboratory temperature.

The culture will be carried out by inclusion in Trypticase soybeanmedium and agar at 37±1° C. for 24 to 48 hours

Before the incubation, the agars are inoculated with a Staphylococcusaureus culture (8×10⁴ CFU), this strain having been chosen asmicroorganism representative of the buccal medium.

Controls free of silicone elastomer biocides of the same type as systemsaccording to Examples 1 to 6 are used.

Results

Biocidal silicone systems Control Ex. 1 to 6 Culture after 6 h Numerouscolonies A few colonies of contact (about 300 CFU/dish) survive (about300 CFU/dish) Culture after 24 h Growth on the All negative of contactsilicones (about 100 CFU/dish) Culture after 3 days Growth on the Allnegative of contact silicones (about 36 CFU/dish) Culture after 7 daysAll negative of contact

What is claimed is:
 1. A silicone elastomer system which comprises: I.at least one polyorganosiloxane (POS) composition comprising apolyaddition silicone composition capable of hardening to an elastomerby hydrosilation, said polyaddition silicone composition comprising:(I_(a)) at least one diorganopolysiloxane oil having, per molecule, atleast two alkenyl groups linked to the silicon; (I_(b)) at least onediorganopolysiloxane oil having, per molecule, at least three hydrogenatoms linked to the silicon; (I_(c)) a catalytically effective quantityof a catalyst which is a compound of a metal of the platinum group; andII. at least one biocidal agent selected from the group consisting of:chloramine B (sodium N-chlorobenzenesulphonamide), chloramine T (sodiumN-chloro-p-toluenesulphonamide), dichldramine T(N,N-dichloro-p-toluenesulphonamide),N-trichloromethylmercapto-4-cyclohexene-1,2-dicarboxylamide, halazone(p-n-dichlorosulphonamidebenzoic acid), N-chlorosuccinide,trichloromelamine, N-chlorohydantoins,1,3-dichloro-5,5′dimethylhydantoin, and mixtures thereof.
 2. The systemaccording to claim 1, wherein the concentration C_(II) of biocidalagent, expressed in % by weight relative to the total mass (I+II), is:C_(II)<1.
 3. The system according to claim 2, wherein the concentrationof biocidal agent is: C_(II)≦0.8.
 4. The system according to claim 4,wherein the concentration of biocidal agent is: C_(II)≦0.5.
 5. Thesystem according to claim 1, wherein the POS composition (I) comprisesin addition, one or more functional additives (I_(d)) selected from thegroup consisting of: inhibitors of the polyaddition crosslinkingreaction; reinforcing and/or semireinforcing and/or bulking fillers,plasticizing agents, and mixtures thereof.
 6. The system according toclaim 1, wherein the POS composition (I) is a bicomponent compositionA-B, a precursor of the elastomer crosslinked at room temperature or byheat, by mixing components A and B, which are not hardenable separately.7. The system according to claim which is obtained by mixing the POScomposition (I) with the biocidal agent (II) in the form of a suspensionor a solution.
 8. The system according to claim 1, wherein the biocidalagent (II) is combined with at least one antiseptic auxiliary agent(III) different from said biocidal agent (II) and optionally at leastone sequestering activator.
 9. The system according to claim 1, whereinthe biocidal agent (II) is tree of inhibitory activity on thecrosslinking of the POS composition (I).
 10. The system according toclaim 1, wherein: the POS composition (I) comprises: (I_(a)): at leastone diorganopolysiloxane oil blocked at each end of its chain by avinyldiorganosiloxyl unit in which the organic radicals linked to thesilicon atoms are chosen from methyl, ethyl and phenyl radicals, atleast 60 mol % of these radicals being methyl radicals, having aviscosity of 100 to 500 000 mPa·s at 25° C.; (I_(b)): at least oneorganohydrogenopolysiloxane selected from the group consisting of linearor lattice liquid copolymers and homopolymers having per molecule atleast three hydrogen atoms linked to different silicon atoms and inwhich the organic radicals linked to the silicon atoms are selected frommethyl or ethyl radicals and at least 60% mole of these radicals beingmethyl radicals, the product (I_(b)) being used in a quantity such thatthe molar ratio of the hydride functions to the vinyl groups is between1.1 and 4; (I_(c)) a catalytically effective quantity of a platinumcatalyst; (I_(d)) one or more functional additives comprising silicas,aluminas, silicates, vinyl disiloxanes, liquid paraffins, paraffins ormixtures thereof; the biocidal agent (II) comprises a chloramine; andthe biocidal agent (II) is optionally combined with an antisepticauxiliary agent (III), optionally supplemented with anactivator-sequestrant.
 11. The system according to claim 10, wherein thebiocidal agent (II) comprises sodium tosylchloramide, the antisepticauxiliary agent (III) comprises a benzalkonium chloride and theactivator-sequestrant comprises EDTA.
 12. A material for taking animpression, which comprises a system according to, claim
 1. 13. Thematerial according to claim 12, which additionally comprises at leastone adjuvant selected from the group consisting of sweeteners,flavourings, colourings, anti-inflammatory agents, isotonic products,and mixtures thereof.
 14. A process for preparing the system accordingto claim 1, comprising mixing the POS compounds (I), the biocidal agent(II) and any optional ingredients.
 15. A process for preparing a systemaccording to claim 1 for taking a dental impression, comprisinginitiating crosslinking of the silicone elastomer, taking the dentalimpression and allowing the crosslinking to continue until the elastomeris hardened.
 16. The system according to claim 1, wherein theN-chlorohydantoins comprise 1-bromo-3-chloro-5,5′-dimethyl hydantoin or1,3-dichloro-5,5′-dimethylhydantoin.